Ionisation Energies

Question 1

Definition of first ionisation energy

Answer 1

The energy needed to remove one mole of electrons from one mole of atoms in their gaseous state to form 1+ ions (also in their gaseous state)

Question 2

Second ionisation energy

Answer 2

The energy needed to remove one mole of electrons from one mole of 1+ ions in their gaseous state to form one mole of 2+ ions (also in their gaseous state)

Question 3

How is greater ionisation energy achieved?

Answer 3

By having a greater attractions between the outer electrons and the nucleus. electrons attracted to the positive protons in the nucleus.

Question 4

What are the 3 factors that affect ionisation energy

Answer 4

• The distance between the nucleus and the outer electrons. As the atomic radius increases the force of attractions between the nucleus and outer electrons decreases
• Nucleus charge. The greater the amount of protons, the greater the force attraction between the outer electrons and the nucleus
• Shielding. Electrons in the outer shells are repelled by the electrons in the inner shell. Shielding reduces the attraction between the outer electrons and the nucleus

Question 5

What do successive ionisation energies tell us about how electrons are arranged in atoms

Answer 5

When removing electrons in the outer shell, the remaining are pulled slightly closely to the nucleus causing greater attractions between the electrons and the nucleus to occur causing the ionisation energy to increase. electrons in the first shell experience less shielding which means they have a greater attraction to the nucleus compared to the second shell

Question 6

Why does the first ionisation energy decrease as we go down a group

Answer 6

Atomic radius increases - the outer electron shell is futher away from the nucleus
The number of internal energy levels also increases - more shielding between the nucleus and the outer electrons

Both mean that going down a group the attraction between the nucleus and outer electrons decreases causing the first ionisation energy to fall. Nuclear charge increases

Question 7

why does the first ionisation energy increase across a period

Answer 7

Nuclear charge increases as the protons increases. This increases the attraction between the nucleus and the electrons. Because the atomic radius decreases across a period. Outer electrons more attracted to the nucleus. Sheild is similar for each elements

Question 8

Dips in the first ionisation energy trend in beryllium and boron

Answer 8

As the fifth electron in boron is in the 2p subshell, which is further away from the nucleus than the 2s subshell of beryllium

Question 9

Dips in the first ionisation energy trend in nitrogen and oxygen

Answer 9

due to spin-pair repulsion in the 2px orbital of oxygen. In oxygen, there are 2 electrons in the 2px orbital, so the repulsion between those electrons makes it slightly easier for one of those electrons to be removed